A machine, as used herein, is any apparatus that can be controlled by an input signal (input). The input signal can be associated with physical quantities, such as voltages, pressures, forces, etc. The machine produces an output signal (output). The output can represent a motion of the machine and can be associated with other physical quantities, such as currents, flows, velocities, positions. Typically, the output is related to a part or all of the previous output signals, and to a part or all of the previous and current input signals. However, the outputted motion of the machine may not be realizable due to constraints on the machine during its operation. The input and output are processed by a controller.
The operation of the machine can be modeled by a set of equations representing changes of the output over time as functions of current and previous inputs and previous outputs. During the operation, the machine can be defined by a state of the machine. The state of the machine is any set of information, in general time varying, that together with the model and future inputs, can define future motion. For example, the state of the machine can include an appropriate subset of current and past inputs and outputs.
The controller for the machine includes a processor for performing a method, and a memory for storing the model. The method is performed during fixed or variable periods. The controller receives the machine output and the machine motion. The controller uses the output and motion to generate the input for the machine.
The machine is subject to constraints, which can be related to the physical environment, machine parts, and machine operational limits. The method is predictive when the controller generates the optimal motion based on the model, a current state of the machine, a desired future behavior of the machine, and the constraints. The controller solves an optimal control problem for a future time starting from the current time.
Some known methods are based on model predictive control (MPC), e.g., U.S. Pat. Nos. 6,807,510, and 7,454,253, where an optimal control problem for a future time is based on the model, the current state, the desired motion, and the constraints. Due to the presence of constraints, unconstrained MPC cannot be applied in that context, see U.S. Pat. No. 7,050,863.
The control problem can be converted to a constrained quadratic programming (QP) problem solved by a constrained optimization procedure. For example, a U.S. 2006/0282177 describes an interior point method for solving the QP problem, and U.S. Pat. No. 7,152,023 describes an active set method. Those methods are computationally complex, e.g., the methods use complex matrix factorization ill-suited for the embedded processors.